1. Field of the Invention
The present invention relates to a force/torque sensor and especially to a monolithically integrated force/torque sensor.
2. Description of Prior Art
The prior art discloses a great number of force sensors. Known monolithically integrated force sensors work on the basis of the piezoelectric effect. Such sensors comprise a piezoelectric converter which converts a force acting thereon into a voltage. Hence, a sensor signal indicative of the force applied can be obtained by detecting this voltage.
It is the object of the present invention to provide a new monolithically integrated force/torque sensor having an improved sensitivity and an improved response.
This object is achieved by a monolithically integrated force/torque sensor comprising a semiconductor region which is adapted to be subjected to a force or torque. Two control electrodes are provided on a first and a second side of the semiconductor region, these first and second sides being arranged in spaced, opposed relationship with one another. A current can be produced between the control electrodes. In addition, two sensor electrodes are provided, which are arranged on a third and a fourth side of the semiconductor region, these third and fourth sides being arranged in spaced, opposed relationship with one another and extend essentially at right angles to said first and second sides. A force or torque applied to the semiconductor region is determinable by detecting a voltage present between the sensor electrodes when a current flows between the control electrodes. The semiconductor region is formed by the channel of a field effect transistor, the drain an source electrodes of said field effect transistor defining the control electrodes.
The present invention is based on the finding that, when a force acts on the semiconductor region, a direction of lower resistance will be created parallel to the direction of dilation, i.e. the direction in which the interatomic distances are enlarged by the action of force. This direction of lower resistance causes a deflection of the current present between the two control electrodes. When this direction of lower resistance between the two sensor contacts, which are located on the third and fourth sides of the semiconductor region, is oriented in a suitable manner, respective charges of opposite polarity will be produced on the third and fourth sides; these charges can be measured as a voltage difference between the sensor contacts.
According to one embodiment of the present invention, the semiconductor region is doped in a suitable manner for permitting the flow of a current between the two control contacts. According to the present invention the integrated force sensor is formed by a field effect transistor, the drain electrode and the source electrode of this field effect transistor being used as the two control contacts. By means of the drain electrode, the source electrode and the gate electrode, a suitable drain current, i.e. a suitable current between the two control contacts, can be adjusted. The opposed longitudinal sides of the channel region have additionally attached thereto the sensor contacts, the channel region being used as the semiconductor region of the sensor according to the present invention.